The objective of the proposed project is to understand the role of non-pyrimidine dimer damage in the biological effects of ultraviolet irradiation. This study will make use of a DNA-binding protein isolated from human placenta and specific for non-dimer UV- or X-ray induced damage. This protein will be employed to protect this non-dimer damage while the DNA is digested with DNase I. Oligonucleotide fragments containing damage will be separated from undamaged fragments by nitrocellulose filtration. Damage-containing fragments will be digested enzymatically and isolated bases from thin layer chromatograms will be analyzed. In addition, the fate of the non-dimer damage in irradiated cells will be examined by using the binding protein as a probe for the presence of such damage in the DNA. This work will be carried out with human fibroblasts as well as with bacterial cells.